1. Field of the Invention
The present invention relates to a rotational position sensor for detecting the rotational position of a rotating axis of a throttle valve used in an internal combustion engine, for example, and more particularly to a non-contact rotational position sensor.
The present invention also relates to a throttle valve assembly including the non-contact rotational position sensor.
2. Description of the Related Art
Conventional rotational position sensors of the above-mentioned type are disclosed in Japanese Patent Nos. 2842482 and 2920179 and U.S. Pat. Nos. 5,528,139, 5,789,917 and 6,137,288.
Those prior-art sensors are based on the fact that, taking the permanent magnet side as a rotor, the circumferential magnetic flux density in a stator is linearly distributed relative to the rotating direction of the rotor. To avoid as perfect as possible a magnetic field distribution in the stator from being affected by the rotational position of the rotor to which the magnet is attached, confronting surfaces of the rotor and the stator are shaped such that their lengths are even in a direction perpendicular to the rotating direction of the rotor.
Because of such a limitation imposed on shapes of the confronting surfaces of the rotor and the stator, the conventional rotational position sensors have a problem that flexibility in design is low when the sensors are designed to be adapted for target equipment to which the sensors are attached.
Accordingly, it is an object of the present invention to provide a non-contact rotational position sensor which is able to operate with satisfactory performance even when confronting surfaces of magnetic paths on the stator side and the rotor side are not shaped such that their lengths are even in a direction perpendicular to the rotor rotating direction.
To achieve the above object, according to one aspect of the present invention, part of a stator-side magnetic path is formed by, e.g., a pair of magnetic plates arranged to sandwich an annular or semi-annular permanent magnet therebetween, which constitutes a rotor. A magnetic flux converging portion serving as a portion to concentrate a magnetic flux is provided midway a closed magnetic path formed through the stator-side magnetic path. A magnetic sensitive device is disposed in the magnetic flux concentrating (converging) portion.
According to another aspect of the present invention, an annular or semi-annular permanent magnet is attached to an end of a rotating shaft of a throttle valve, and a pair of magnetic substance assemblies sandwiching the permanent magnet therebetween to form magnetic paths are attached to a resin cover which is in turn attached to a body of the throttle valve. A magnetic flux converging portion is provided in each of the magnetic substance assemblies, and a magnetic sensitive device is disposed in the magnetic flux converging portion.
More specifically, the annular or semi-annular permanent magnet is detachably attached to the rotating shaft, and at least one of the magnetic substance assemblies has a hole formed at the center thereof and having a diameter greater than a diameter of the rotating shaft, but smaller than an inner diameter of the permanent magnet.